Epoxy resin composition-containing prepregs have been known as the adhesive materials used in production of printed wiring boards. Such a prepreg is produced by impregnating a substrate such as glass cloth with a varnish of epoxy resin composition and drying the resulting substrate.
And, a printed wiring board is produced by forming a metal clad laminate by means of preparing a laminated sheet by piling a particular number of the prepregs and placing a metal foil additionally on at least one outermost layer and heat press-molding the laminated sheet under, forming holes for through holes in the clad laminate obtained for example by drilling, forming through holes by plating the holes, and forming a particular circuit pattern on the metal clad laminate surface by etching the metal foil thereon.
The multilayer printed wiring board is obtained by using such a printed wiring board and a prepreg. Specifically, a multilayer printed wiring board is obtained by placing a particular number of prepregs on one or both faces of the printed wiring board and additionally a metal foil on the outermost layers and heat press-molding the laminate.
Holes are formed in the multilayer printed wiring board; throughholes are formed by plating the holes; and a multilayer printed wiring board having a circuit on the outermost surfaces is prepared by forming a circuit pattern on the metal foil on the metal clad laminate surface by etching.
Dicyandiamide-based curing agents have been used widely as the curing agent for the epoxy resins used in preparing such a prepreg. However, unfavorably, epoxy resins cured by using such a dicyandiamide-based curing agent were less heat resistant and thus, the resulting printed wiring boards were lower in heat resistance.
It is known to use a phenolic curing agent such as cresol novolak resin, phenolic novolak resin, or bisphenol A-based epoxy resin as the curing agent for epoxy resin for improvement of the heat resistance of printed wiring boards (see, e.g., Patent Document 1).
However, epoxy resin compositions containing a phenolic curing agent as the curing agent for epoxy resin had a problem of low moldability, compared to epoxy resin compositions containing a dicyandiamide-based curing agent from the following reasons:
Specifically, it is difficult to keep the board thickness constant, because the resin components contained in the prepreg prepared by using a phenolic curing agent as the curing agent epoxy resin is too low in viscosity. It is also difficult to adjust the timing of pressurization during curing, because the resin becomes very viscous, giving a gel by three-dimensional crosslinking, at a particular time point. As a result, there was a problem that the range of the moldable curing (gel time) is narrow (the range of favorable molding condition is limited).
An epoxy resin composition for printed wiring board containing an imidazole-silane compound, prepared by using a phenolic curing agent containing a bifunctional or lower phenolic curing agent in an amount of 20 to 50% is known as a method of improving the moldability of the phenolic curing agent-containing prepregs (see e.g., Patent Document 2).
However, although the prepreg obtained by using the epoxy resin composition for printed wiring board described in Patent Document 2 was improved in moldability, the adhesiveness between prepregs and also between the prepreg and circuit formed for example with copper foil was insufficient, unfavorably.    Patent Document 1: Japanese Unexamined Patent Publication No. 8-151507    Patent Document 2: Japanese Unexamined Patent Publication No. 2004-115634